The invention relates to a sensor for detecting the temperature of a fluid, in particular a flowing liquid or gaseous medium, in the hollow space of a housing. A temperature measuring element, connectable to an evaluation device via a plug arrangement, is arranged in a protective tube of a sensor housing, which is closed on one end, with a firmly inserted connection piece. The protective tube projects at least partially into an opening of the hollow space of the housing that is sealed off from the outside atmosphere using an elastic O-ring.
From German published patent application DE 33 16 995 A1, a temperature detection device is known with a temperature sensor, that is held in a housing and projects with its measurement region out of one end of the housing. Means are provided for attachment of the one end into an opening of a hollow structure containing a liquid or gaseous medium. According to DE 33 16 995 A1, a temperature detection device is provided, which is easy to install even by non-specialized persons and is to be connected securely to an evaluation and display device. A penetration into the allocated housing of a liquid or gaseous medium that impairs the functionality must be prevented to a certain degree.
In order to solve the problem, it is provided according to DE 33 16 995 A1 that a housing constructed as a plastic injection-molded part is formed in two pieces. The temperature sensor held on one end of the one housing piece is enclosed in an airtight manner by the housing piece up to the measurement region and is connected with two pin-shaped contact pieces held in the one housing piece. The other end of the one housing piece is constructed as a plug, to which an available plug receptacle is allocated, which is arranged on one end of the other housing piece that has two socket-shaped contact pieces. A line connected to the evaluation and display device can be supplied via the other end of the other housing piece and equipped so that it can be connected to the socket-shaped contact pieces. The two housing pieces are provided with catch mechanisms in the region of the plug and the plug receptacle for a defined connection. A sealing mechanism is allocated to the two housing pieces in the region of the plug and the plug receptacle for the purpose of preventing the penetration of a liquid or gaseous medium into the contact zone. This involves a relatively expensive construction, which requires a high degree of expertise during construction.
Starting from a screw-in sensor, as known from the above-mentioned DE 33 16 995 A1, an object of the invention is take temperature measurements using a screw-in sensor in fluids, i.e., various liquid or gaseous media. Here, a socket mounted directly on the sensor should be used, especially one according to the German Industrial Standard (DIN) 72585.
This object is achieved according to the invention in that the measuring element is arranged in the region of the tip of the protective tube on one end of a longitudinally extended circuit board and is connected via strip conductors to the plug arrangement positioned on the opposite end of the circuit board. It has proven to be advantageous that with a sensor of this type, a small construction space, a rapid response behavior, and a high vibration-resistance are obtained.
In a preferred embodiment of the invention, the plug arrangement is surrounded by a screw sheath of the sensor housing, which is firmly connected to the protective tube and which is provided with a threading that projects into the housing of the hollow space for the purpose of attachment. Here, the screw sheath has a flange extending in the radial direction, which functions as a pressing surface for an O-ring that seals off the opening of the hollow space-housing. The screw sheath is provided, on its side facing away from the protective tube, with an annular edge arranged coaxially to the screw sheath threading, for attaching a connection piece essentially made out of plastic, wherein plug contacts of the plug arrangement project into the connection piece opened to the outside. Advantageously, the connection piece is arrested against axial shifting by an annular flange of the edge of the screw sheath in its plug-in position.
The sensor thus comprises a screw sheath, which receives a plug arrangement. The edge of the screw sheath is placed around the plug arrangement with the connection piece using a special tool in a work operation, and at the same time, severalxe2x80x94for example, threexe2x80x94lock beads are applied to prevent turning. The positioning of the lock beads on the correspondingly provided recesses in the connection piece for the plug arrangement is achieved via an opposing plug that is integrated in the tool, by which the function as well as the insulation of the sensor can be tested simultaneously during pressing. A longitudinally extending circuit board is soldered to the plug arrangement and extends up into the tip of the protective tube and accommodates the measuring element of the temperature sensor.
The functional unit formed by the plug arrangement, screw sheath, and connection piece serves for connection of an external plug for the electrical connection to an evaluation unit and display device (and/or controller) for the temperature signal. Among those skilled in the art, the functional unit is therefore also called a plug socket.
As a temperature-measuring element, a component provided with a connection wires or a surface-mountable component (SMD) can be used, since the necessary connection soldering surfaces are provided for both cases. The temperature-measuring element is, for example, a thin-film platinum element or an NTC-element. It is advantageously embedded in heat-conducting paste, in order to ensure a rapid response. Over the measuring element and the circuit board a shrinkable tube is applied for insulation and for the mechanical protection of the element.